the logic board mounted 0.022F 5.5V capacitor used to supply power to hold PRAM settings while changing the battery.
Unlike most PowerBooks and desktop Macs which have PRAM batteries and are capable of holding parameter RAM settings for extended periods, the iBook G3 & iBook G4 use a small capacitor which only provides around 20seconds of power which is considered sufficient to allow batteries to be switched without loosing settings. If this capacitor fails, settings will not be held and logic board behavior can become erratic. (from a website that sells them here in uk)
the big problem there is you can basically only check if the capacitor is working if the battery works
mine died not long ago but battery was just , just fine about 30min-1hr and suddenly one morning all dead , logic board looked like there had been a nuclear explosion inside , a known prob these failing logic boards on the ibooks ,usually they failed after the apple care period and apple did know that too like so often with their products,but i just like them so i look for another one